Archive Notice - OSHA Archive

NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.

OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at

June 13, 1996

Robb Menzies, President
ACE Systems, Ltd.
945 Malory Street
Lafayette, Colorado 80026

Dear Mr. Menzies:

We are in receipt of your letter forwarded to our office from Dr. Gerry Ryan, Assistant Regional Administrator for Technical Support in the Occupational Safety and Health Administration (OSHA) Region VIII. This letter will only address the respirator concerns expressed in your original letter to Region VIII. We understand that the other issues you raised were addressed by Dr. Ryan in his response to you dated February 27, 1996.

Your request first of all is not without precedent. We are aware that there have been several studies in the literature that support the use of organic vapor charcoal filters as effective against isocyanates. As you are aware, OSHA requires the National Institute for Occupational Safety and Health (NIOSH) certification of respirators and that for contaminants with poor warning properties NIOSH specifies that a supplied air respirator must be used. NIOSH has, however, approved the use of an end-of-service-life indicator for mercury vapor. Mercury vapor also has poor warning properties.

OSHA, in the case of benzene, with its poor warning properties, has allowed the use of organic vapor cartridges with a half mask elastomeric respirator (29 CFR 1910.1028). In the preamble to the benzene standard, OSHA stated the following:

"For lower concentrations of benzene, OSHA proposes to permit the use of air purifying respirators provided that the filter element is replaced at the beginning of each workshift. Benzene has poor warning properties at low levels, and OSHA is aware that MSHA/NIOSH would not approve the use of air-purifying respirators in this situation because the users would be unable to detect the benzene if breakthrough occurs. However, OSHA believes that filter elements of the type approved by MSHA/NIOSH for use with organic vapors would provide sufficient service life for the intended application as prescribed in Table 1 if replaced with the required frequency."

You indicated that, based upon your conversations with NIOSH, their certification of your specially treated charcoal filter with an optional end-of-service-life indicator would be delayed. The delay is due to resource demands posed by a backlog of certification requests resulting from NIOSH's recently revised certification procedures that are codified at 42 CFR Part 84. We have contacted NIOSH concerning this issue and suggest that since the unit apparently is already patented in the United States and has been sent for certification in Canada, the unit should also be submitted to NIOSH for certification, unless problems with the unit have surfaced in the Canadian certification process. We spoke with NIOSH regarding your letter and were told that you should contact Larry Reed with NIOSH in Cincinnati, Ohio. Mr. Reed can be contacted at (513) 533-8304 or FAX at (513) 533-8588. A copy of your letter and this response will be forwarded to Mr. Reed.

Concerning our acceptance of a Canadian approval, we are not aware of any respirator certification procedure in Canada. It has been our understanding that in Canada, the standard practice is to accept and use the NIOSH respirator certification process. If however, Canada does certify respirators and certifies your charcoal filters and the end-of-service-life indicator, that testing and certification information should be provided to NIOSH along with your application. Our respirator standard specifies only NIOSH approval and certification. OSHA would not be able to accept the certification of a respirator by another governmental agency outside the United States unless a cooperative agreement or a memorandum of understanding was reached between NIOSH and the certification group in another country.

One other point must be mentioned. OSHA can only require the use of respiratory protection where we can document that an overexposure has or is likely to occur. In the case of spray painting in autobody shops, our sampling data from this industry has found virtually no overexposures to isocyanates. Workers could currently wear a half mask respirator with organic vapor cartridges and be within our requirements provided the employees were not exposed to isocyanates above our permissible exposure limits. An employer should, under these circumstances, conduct periodic monitoring for isocyanates to assure that the worker exposure to isocyanates remain below the permissible exposure limit.

We hope this information provides you some assistance to a complicated issue. If we can be of any further assistance please contact the Office of Health Compliance Assistance at (202) 219-8036.


John B. Miles, Jr., Director
Directorate of Compliance Programs

February 27, 1996

Robb Menzies
ACE Systems, LTD.
945 Malory St.
Lafayette, Colorado 80026

Dear Mr. Menzies:

Thank you for your letter and the subsequent information that you sent to us regarding respiratory protection in auto body shops using isocyanate catalyzed urethane paints. You raised a number of concerns and questions regarding isocyanate PEL's, air sampling protocols, respiratory protection, and governmental protocols for approval of respirators. We also understand that you have been involved in an initial phase of a NIOSH health hazard evaluation (HHE) of autobody shops in this area, and that several additional evaluation phases are planned for the future.

Before I address your concerns, I want to first state that the following discussion is intended to address the hazards associated with isocyanates in the automotive spray painting industry only. The hazards associated with isocyanate exposures in other types of industries and applications present higher levels of exposure to the isocyanate monomers which pose additional problems and solutions.

Your first concern dealt with the inadequacy of the current PEL's for isocyanates and that workers are being placed at risk. You further stated that the dermal route of exposure may be as important or more important than inhalation exposures. As you are aware, the OSHA PEL's, NIOSH REL's, and ACGIH TLV's only cover isocyanate monomers. Isocyanate oligomers and polymers are not covered by these recommendations. OSHA has listed occupational asthma as one of the agency's priorities in our Priority Planning Process. This is an internal planning process for identifying initiatives in need for regulatory development or some form of non-regulatory action. Isocyanates would probably play a major role in any occupational asthma initiative. It is extremely early in the planning process. A decision of how and when to address this issue has not been made. You should feel free to provide the agency comments on the appropriateness of a new initiative on isocyanates, by writing the OSHA National Office. Should the agency decide to begin the rule making process, I would strongly encourage you to participate, by providing comments, data, recommendations, etc. to the public record.

In the meantime, I would suggest that you advise your clients on two levels, what is regulatory required, and what would be prudent practice. The medical and safety and health community recognize that the oligomers and polymers of isocyanates are hazardous. While the literature appears to indicate that these compounds carry a lesser risk than their monomer counterparts, they do carry with them some risk of respiratory sensitization. The HSE of the UK has a total isocyanate PEL of 20ug/m(3). This standard covers all forms and species of isocyanates. Several organizations including one OSHA state plan have PEL's on HDI polyisocyanates. The state of Oregon's PEL is 0.5 mg/m(3) (8hr TWA) and 1.0 mg/m(3) (Ceiling). France has a STEL of 1.0 mg/m(3) and Sweden has a PEL of 0.09 mg/m(3) (8hr TWA) and a 5 minute STEL of 0.2 mg/m(3). Several manufactures also have similar recommendations. Mobay recommends a STEL of 1.0 mg/m(3) and Miles and Bayer recommend to use the limits for TDI monomer for mixed isocyanates. As a safety and health professional this latter recommendation makes sense. It simplifies the situation by aggregating your data together and comparing the results to one value while treating the less hazardous species (oligomers and polymers) the same as the monomers. Until such time that good data and or PEL's exists for the oligomers and polymers, it would be prudent to assume the worst.

As far as dermal exposures are concerned, I concur with you, that they pose a potential for being a significant source of monomer exposures, particularly during cleaning of the spray rig equipment. OSHA would expect that employees be protected from skin contact with isocyanates and the solvents that they would be dissolved in. 29CFR 1910.132(a) would require at a minimum that appropriate gloves be worn to avoid skin contact.

In order to make any assessment of potential risk, recommend the appropriate level of respiratory protection, or assess personal work practices, etc. one needs to quantify the level of isocyanate exposures. As you have indicated, there are several air sampling and analytical methods that are currently in use. The OSHA sampling method involves the use of an impregnated filter while NIOSH is using the impinger method. Various studies have evaluated the two methods. Some have found that the impinger method captures a greater amount of the isocyanate complex while others have found the opposite. The OSHA impregnated filter method has been validated for the monomers but since we do not regulate the oligomers and polymers the method has not been validated for these species. OSHA does not mandate any particular method. You are free to choose any method that you feel gives you reliable results. If you want to use the Canadian IRSST method since it has been validated for monomers, oligomers, and polymers, you certainly are free to do so.

Once you are satisfied that you have adequately characterized the extent of the isocyanate exposures, the next question in need of answering is what level of respiratory protection is warranted. NIOSH's interim HHE report has indicated that the painters in the autobody shops covered by their survey were not overexposed to isocyanate monomers. Studies in the literature, have tended to agree that monomer exposures to workers in autobody shops typically do not exceed the OSHA, NIOSH or ACGIH guidelines. OSHA's field experience has been similar. However, this experience does not always hold true. NIOSH, OSHA, and the literature have found instances where spray painters have been overexposed to the monomers. This fact points to the importance to adequately monitor each work place for actual experience.

Regardless, once exposures are characterized, OSHA would only mandate respiratory protection when the concentrations of isocyanate monomer, or some other constituent in the paint, ie., solvent or pigment, exceed ACGIH guidelines, or OSHA PEL's. In the case of isocyanate monomer overexposure, OSHA currently mandates the use of air-supplied respirators, as approved by NIOSH. This high protection level is due to the poor warning properties that isocyanates possess. If a company was using respiratory protection in instances where they were not legally mandated and some monomer was present, OSHA would require that a respiratory protection program in accordance with 29CFR 1910.134 be instituted, but would not mandate airline respirators just because of the presence of isocyanates (again, this assumes that the monomer concentrations are below the OSHA PEL's and ACGIH's TLV's).

We are aware that a number of studies have indicated that charcoal (OV) filters, with and without pre-filters have been found to be effective in protecting against isocyanates. They have also found that once absorbed, the isocyanate complex is very stable and does not migrate readily on the filter. The problem that isocyanates pose for the NIOSH certification process is the lack of warning properties. These studies have also found that the typical paint solvents, ie., toluene, acetone, ethyl acetate, cellosolve acetate, which do have good warning properties, breakthrough long before the isocyanates. This observation has lead a number of investigators to recommend that the warning properties of the solvents be used as surrogates for the isocyanates. As you have described, we understand that a patent for a specially treated charcoal filter, with optional end-of-life indicator element has been issued in this country. This filter has also been submitted for certification and use in Canada. It has not been submitted to NIOSH for certification at this time. The issue that you raised on whether the warning properties for the solvents can be used and thus whether negative pressure respirators can be used has been sent to our National Office for their determination. Likewise the issue of whether we would "accept" this new cartridge in this country if and when Canada certifies it has also been referred. In the meantime, I would anticipate that most of your painting operations would not be over the PEL's or TLV's for the monomers, therefore, the use of negative pressure respirators would be acceptable as long as a respiratory protection program in accordance with 29CFR 1910.134 was instituted.

Your concern that NIOSH update their testing capability for isocyanates and change their position on warning properties needs to be addressed with NIOSH.

One note of caution, OSHA would expect that regardless of the final results of the NIOSH HHE currently underway in autobody shops in this area, each establishment would be responsible for performing their own evaluation of representative exposure to isocyanates or other contaminants before selection of respiratory protection. The HHE will define worker exposures in certain shops with certain paints and spray booths, and those results should not be applied as representative exposure levels throughout the entire industry. In addition, I would not totally dismiss the use of airline respirators. Many employers have found that an airline respirator system to be cheaper in the long run as compared to the costs of running a negative pressure respirator program, ie., the costs of respirator cartridges being replaced every few days adds up quickly.

I appreciate your concern for work place safety and health. Should you have further questions or concerns do not hesitate to contact us. You will be receiving a response directly from Washington D.C., on the two issues referred.


Gerard Ryan, Ph.D., CIH
Assistant Regional Administrator
for Technical Support